In the Exchange 2010 management shell run the following command to lock the public folders.
In an organization with multiple public folder databases it may take several hours for all public folders in the organization to receive this change via replication.
At a high level the process involves: Of course the reality is that there are many caveats and ways for a public folder migration to go wrong.
Generally speaking you should always refer to the Tech Net article as it will document the latest requirements and limitations for a public folder migration.
However if that decision can't be made, or they are still required for some reason, then a migration to Exchange 2013 can be performed.
Initially Microsoft provided a public folder migration method known as serial migration.